In CT X-ray imaging of a patient, X-rays are used to image internal structure and features of a region of the patient body. The imaging is performed by a CT-imaging system, hereinafter referred to as a “CT scanner”, which generally comprises an X-ray source and an array of closely spaced X-ray detectors positioned to face the X-ray source. The X-ray source and array of detectors are mounted in a gantry so that a person being imaged with the CT scanners, generally lying on an appropriate support couch, can be positioned within the gantry between the X-ray source and the array of detectors. The gantry and couch are moveable relative to each other so that the X-ray source and detector array can be positioned axially, along a “z-axis”, at desired location along the patient's body. The gantry comprises a stationary structure, referred to as a stator, and a rotary element, referred to as a rotor. The rotor is mounted to the stator so that the rotor is rotatable in a plane perpendicular to the z-axis about a center of rotation.
At the present time, X-ray detectors are mounted into a data measurement system cradle, and the cradle is then mounted onto the CT rotor. In the past the rotation speed of the rotor was one revolution per second or less. At these speeds the centrifugal forces on the cradle were moderate and warping of the cradle was not a great issue. However, the rotational speed of the rotor is approaching 4 revolutions per second, which results in 16 times more centrifugal force when compared to one revolution per second. One way to combat the force is to make the cradle structure more substantial, but that may increase cost and cause the cradle to be heavy.
The large force centrifugal has negative effect on CT imaging. As it is well known, in the CT scanner it is very important that the detectors be in precise position relative to the focal spot of the X-rays radiation and the center of the rotation. Furthermore, the anti-scatter grids in the scanner should be aligned such that they all point at the focal spot. The large centrifugal forces on the cradle will cause detectors motion, which may results in image artifacts.
On the other side, at present time the x-ray tube used in CT scanner is a self-contained unit with its own x-ray shielding, structural housing and motor stator. The tube assembly is then mounted on a tube shelf, which may or may not be integral to the rotor itself. When a tube is replaced the x-ray shield and structural housing are also replaced even though these parts did not fail. For some CT scanner, the x-ray tube shelf has been known to move under centrifugal force resulting in an undesirable motion of the focal spot, which introduces image artifacts.
Therefore there is a need to provide a rotor with new structure that reduces relative motion between the focal spot of an X-ray radiation source and detector modules so as to reduce imaging artifacts.